Exploring Galactic open clusters with Gaia. II Dynamical Evolution and Stellar Population Properties in Fifteen Nearby Open Clusters

Stellar mass governs stellar evolution and the distribution of stellar masses plays a central role in the dynamical evolution of stellar clusters. Using high-precision astrometry and photometry from Gaia DR3, we investigate mass segregation and the present-day mass function (PDMF) in fifteen nearby open clusters. Single and binary stars are identified from the color magnitude diagram, and stellar masses for single stars are derived from a cubic spline relation with G-band magnitude, while binary component masses are estimated via a simulation-based inference method. Based on these mass estimates, mass segregation is quantified using the minimum spanning tree technique, and the PDMF is characterized through power-law fitting. We detect significant mass segregation in all clusters. Systems lacking very massive stars exhibit weaker segregation affecting a larger fraction of the population, whereas clusters hosting a small number of very massive stars show strong central concentration of these objects. The PDMF follows a power law with a slope of 2.01, consistent with the canonical Kroupa initial mass function. The strength of mass segregation correlates with the mass of the most segregated stars. Strong segregation observed in very young clusters supports a primordial origin, while older clusters display signatures of dynamical mass segregation at lower masses and evidence of binary disruption. A low-mass break in the PDMF observed in most clusters, if not due to incompleteness, may reflect early gas expulsion in initially mass-segregated systems.